Process for isomerizing paraffinic hydrocarbons



Glenn 0. Michaels, Park Forest,

United States Patent 3,206,525 PROCESS FOR ISOMERIZING PARAFFINICHYDROCARBONS and John Mooi, Homewood, 11]., and Carl D. Keith, Summit,N.J., assignors to Sinclair Refining Company No Drawing. Filed Oct. 26,1960, Ser. No. 65,014 10 Claims. (Cl. 260683.66)

This application is a continuation-in-part of applica tion Serial No.851,526, filed November 9, 1959, and now abandoned.

The invention relates to the isomerization of n-paraffinic hydrocarbonsto obtain good yields of branched chain aliphatic structures and isparticularly concerned With the catalytic isomerization of n-paraflinichydrocarbons employing a hydrocarbon conversion catalyst consistingessentially of a noble metal, an activity enhancing compound andalumina. The branched chain aliphatic structures, e.g. isomericstructures of n-parafiins, are particularly useful in providing gasolinecomponents of high octane rating.

In recent years automobile manufacturers have steadily increased thecompression ratios of their spark ignition engines as a means ofobtaining more power and greater efficiency. As the compression ratiosof the engines increase, the hydrocarbon fuel employed must be of higheroctane rating to provide efficient knock-free operation notwithstandingthat fuel octane rating can be increased through the addition oftetraethyl lead, and other undesirable aspects of engine operation, forinstance pre-ignition, can be overcome by the use of other additivecomponents. Thus, the problem remains for petroleum refiners to producehigher octane base hydrocarbon fuels under economically feasibleconditions.

These refiners now have installed a substantial number of units forreforming straight run petroleum fractions in the presence of freehydrogen and over a platinum metal-alumina catalyst to obtain relativelyhigh octane products. Primarily these products, frequently calledreformates, are blended with other gasoline components such as thermaland catalytically cracked gasolines, alkylates, etc., and additives suchas tetraethyl lead in obtaining present-day motor fuels. The reformingoperation has a number of disadvantages. First, as the octane ratings ofthe blended engine fuels rise, the octane quality of the reformate mustalso increase if the blends be otherwise unaltered. This increaseresults in a substantial reduction in yield particularly in obtainingreformates having octanes (RON neat) of the order of 10 to 95 or above.When the severity of the operation is increased, the platinummetal-containing catalyst becomes fouled more often with carbonaceousdeposits which requires more frequent regenerations or replacements. Theplatinum metal-alumina catalysts are relatively expensive, and eitherreplacement or withdrawal from use during regeneration materiallyincreases the cost of providing a given volume of reformate. These andother factors affecting the yield-octane number-cost relationship makeit desirable for the refiner to consider various ways in which highoctane hydrocarbon fuel components can be obtained by employingprocessing methods other than the platinum metal-alumina catalystreforming operation.

One method now under consideration by petroleum refiners for obtainingstocks of higher octane value involves the isomerization of C or C to Cn-paraflinic hydrocarbons, that is, n-butane, n-pentane, n-hexane,nheptane, n-octane, n-nonane and their mixtures with each other and withother hydrocarbons in the same approximate boiling range. In general, asthe side chain branching of these n-paraffins increases, their octaneratings rise. In the process of the present invention we have foundPatented Sept. 14, 1965 catalysts which are useful in the isomerizationof the C to C n-paraflins in the presence of free hydrogen to affordhighly satisfactory yields of isomer products. These catalysts arecharacterized by being sufficiently active to allow the use ofrelatively lower isomerization temperatures and provide for advantageousisomerization equilibrium conditions.

The catalyst used in the process of the present invention includescatalytically effective amounts of a noble or platinum group metal andactivity enhancing or promoting amounts of a component selected from thegroup consisting of H SiF NH BF and Ni(BF supported on an alumina base.The catalyst generally contains about 0.01 to 2 weight percent,preferably 0.1 to 1 weight percent, of one or more of the platinummetals of Group VIII, such as platinum, palladium, or rhodium. The smallamount of noble metal may be present in the metallic form or as asulfide, oxide or other combined form. The metal may interact with otherconstituents of the catalysts, but if during use the noble metal bepresent in metallic form then it is preferred that it be so finelydivided that it is not detectable by X-ray diffraction means, i.e. thatit exists as crystals of less than 50 Angstrom units size. Of the noblemetals platinum, palladium and rhodium are preferred.

The activity enhancing component is surface dispersible on the support.It is employed in amounts sufiicient to enhance the life of the aluminasupport and such amounts are, therefore, preferably added in directproportion to the area of the support. For instance, the amount of theactivity enhancing component will depend upon the specified promotingcomponent employed. Generally, however, the activity enhancing componentwill be employed in a molar ratio to the alumina of about 0.001 to 03:1and preferably from about 0.02 to 0.1:1. When the activity enhancingcomponent contains boron and fluorine, the molar ratio of the fluorineto boron will generally be from about 2 to 6:1. The weight percent ofthe fluorine in the catalyst will generally be from about 0.1 to 15% andpreferably from about 1.5 or 3 to 6 or 7.5 weight percent.

The noble metal and activity enhancing component constituents of thecatalyst are supported on an absorptive alumina base of the activated orcalcined type. The base is usually the major component of the catalyst,generally constituting at least about weight percent on the basis of thecatalyst, preferably at least about to The catalyst base is an activatedor gamma-alumina such as those derived by calcination of amorphoushydrous alumina, alumina monohydrate, alumina trihydrate or theirmixtures. The catalyst base precursor most advantageously is a mixturepredominating in, or containing a major proportion of, for instanceabout 65 to weight percent, one or more of the alumina trihydratesbayerite I, bayerite II (randomite) or gibbsite, and about 5 to 35weight percent of alumina monohydrate (boehmite), amorphous hydrousalumina or their mixture. The alumina base can contain small amounts ofother solid oxides such as silica, magnesia, natural or activated clays(such as kaolinite, montmorillonite, halloysite, etc), titania,zirconia, etc., or their mixtures. Although the components of thecatalyst can vary as stated, a preferred catalyst contains platinum andthe activity enhancing component deposited on activated alumina.

The isomerization reaction conditions used in the method of the presentinvention include a temperature suflicient to maintain the n-paraffinfeed in the vapor phase under the pressure employed. Generally, thistemperature will be from about 500 to 800 F., preferably about 600 to700 F. or 750 F., while the pressure will be superatmospheric forinstance ranging from about 50 to 1500 p.s.i.g., preferably about 200 to1000 p.s.i.g. The catalyst can be used as a fixed, moving or fluidizedbed or in any other convenient type of handling system. The fixed bedsystem seems most advantageous at this time and the space velocity willin most cases be from about 0.25 to 8:1, preferably about 0.75 to 4:1,weight of n-paraffin per weight of catalyst per hour (WI-ISV).

Free or molecular hydrogen must be present in our reaction system andthe hydrogen to n-paraffin molar ratio will usually be from about 0.01to 2011 or more, preferably about 2 to 10:1. Conveniently, the hydrogenconcentration is maintained by recycling hydrogen-rich gases from thereaction zone.

As previously stated the preferred catalyst base material is anactivated or gamma-alumina made by calcining a precursor predominatingin alumina trihydrate. An alumina of this type is disclosed in US.Patent No. 2,838,444. The alumina base is derived from a precursoralumina hydrate composition containing about 65 to 95 weight percent ofone or more of the alumina trihydrate forms gibbsite, bayerite I andbayerite II (randomite) as defined by X-ray diffraction analysis. Thesubstantial balance of the hydrate is amorphous hydrous or monohydratealumina. Trihydrates are present as well defined crystallites, that isthey are crystalline in form when examined by X-ray diffraction means.The crystallite size of the precursor alumina trihydrate is relativelylarge and usually is in the 100 to 1000 Angstrom unit range. Thecalcined alumina has a large portion of its pore volume in the pore sizerange of about 100 to 1000 Angstrom units generally having about 0.1 toabout 0.5 and preferably about 0.15 to about 0.3 cc./g. of pore volumein this range. As described in the patent the calcined catalyst base canbe characterized by large surface area ranging from about 350 to about550 or more square meters/gram when in the virgin state as determined,for example, by the BET adsorption technique. A low area catalyst baseprepared by treating the predominantly trihydrate base precursor isdescribed in U.S. Patent No. 2,838,445. This base when in the virginstate has substantially no pores of radius less than about 10 Angstromunits and the surface area of the catalyst base is less than about 350square meters/ gram and most advantageously is in the range of about 150to 300 square meters/gram.

The platinum group metal component of the catalyst can be added to thealumina base by known procedures. For instance, the platinum metalcomponent can be deposited on a calcined or activated alumina, but it ispreferred to add the platinum metal component to the alumina hydrateprecursor. Thus, platinum can be added through reaction of a halogenplatinum acid, for instance, fiuoro-, chloro-, bromoor iodo-platinicacid, and hydrogen sulfide in an aqueous slurry of the alumina hydrate.The hydrogen sulfide can be employed as a gas or an aqueous solution.Alternatively, the platinum component can be provided by mixing anaqueous platinum sulfide sol with the alumina hydrate. This sol can bemade by reaction in an aqueous medium of a halogen platinic acid withhydrogen sulfide. The alumina hydrate containing the platinum metal canbe dried and calcined usually at a temperature from about 750 to 1300 F.or more to provide the activated or gammaalumina modifications. Theactivity enhancing component can be added to the catalyst in any stageof its preparation. It may be incorporated in the support, either beforeor after the addition of the Group VIII metal. It will usually beapplied by impregnation from solution (water, organic or inorganicsolvents) or from a gas phase. It is frequently added to the catalystafter it has been formed by tabletting or extrusion and calcined. Afterthe activity enhancing component is added in this procedure the catalystcan be recalcined.

Even though our catalyst can be employed directly in the isomerizationsystem, it can be pretreated with free or molecular hydrogen. Forinstance, the catalyst can be heated at temp ratures from about 800 to900 F. in

a slowly flowing stream of hydrogen for a period of time (e.g. 1 to 3hours) sufiicient to activate the catalyst.

The catalyst employed in the process of the present invention can beregenerated employing conventional procedures, for instance bysubjecting it to an oxygencontaining gas at temperatures sufficient toburn off carbon deposited on the catalyst during the conversion ofpetroleum hydrocarbon feedstock. This oxygen-containing gas, e.g. anoxygen-nitrogen mixture, can contain about 0.01 weight percent to 5weight percent oxygen but preferably contains about 0.5 to 1.5 weightpercent oxygen and is introduced at a flow rate such that the maximumtemperature at the site of combustion is below about 1000 F.

The paraffinic feed material employed in our process is generally a C toC n-paraflinic-containing cut derived from crude petroleum hydrocarbons,as by distillation, reforming and extraction processes. The feed can bea blend of n-pentane and n-hexane usually containing about 25 percent ormore of n-hexane and preferably a predominant amount of n-hexane.

The following specific examples will serve to illustrate our inventionbut they are not to be considered limiting.

Example I PREPARATION OF NOBLE METAL ALUMINA CATALYST A noble metalalumina composition of the kind described in US. Patent No. 2,838,444can be employed in preparing the catalyst used in the process of ourinvention. The composition of this patent can be made as follows. Purealuminum metal is dissolved in pure hydrochloric acid, and the resultingsolution is mixed with deionized water to form an aqueous aluminumchloride solution and an alumina gel is prepared equivalent toapproximately 65 grams of A1 0 per liter. A separate deionized watersolution of NH OH is prepared containing approximately 65 grams ofammonia per liter. These two reagents in approximate volume ratio of 1:1are intimately mixed as a flowing stream at a pH of 8.0. The flowingstream is passed to a stoneware container and an alumina hydrate isvisible. The precipitated hydrate is filtered from the mother liquid andwashed to 0.2% chloride by successive filtrations and reslurryings indeionized water until the desired chloride concentration is reached. Ineach reslurrying ammonia is added to give a pH of about 9. The washedhydrate is covered with water in a container and aged at about F. untilit is approximately 70% trihydrate, the remaining being substantially ofthe amorphous or monohydrate forms. The total hydrate composition iscomprised of 42% bayerite, 18% randomite, 11% gibbsite, 20% boehmite,and 9% amorphous as determined by X-ray difiraction analysis. The agedhydrate is mixed with deionized water in a rubber lined container toprovide a slurry of about 7 weight percent A1 0 at a pH of about 8.0. Achloroplatinic acid solution in deionized water (0.102 gram platinum permilliliter) is stirred into the slurry and the slurry is then contactedwith a deionized water solution which has been saturated with H 5 at 78F. to precipitate the platinum. The pH of the slurry is adjusted to 6.0to 6.5 by ammonium hydroxide addition and the solids of the slurry aredried on a horizontal drum drier to give a powder of generally less than20 mesh. The drum drier powder is mixed in a planetary type dough beaterwith sufiicient deionized water to indicate Q5 weight percent water on aCentral Scientific Company Infra-red Moisture Meter containing a wattbulb, Cat. No. 26675. The resulting mixture is forced through a dieplate having holes in diameter bolted to a 3%" Welding Engineers screwextruder. The resulting strands .are broken to particles of lengthvarying generally between about A to 1".

The particles are dried at 230 F. and calcined by heatlng to 925 F. in aflow of nitrogen gas followed by a flow of -air while the composition ismaintained at a temperature in the range of 865 F. to 920 F. Thecomposition thus produced analyzes about 0.6 weight percent of platinumwhich is in sufliciently divided form so as to exhibit by X-raydiffraction studies the substantial absence of crystallites or crystalsof size larger than 50 Angstrom units. After the calcination thecomposition has an area (BET method) within the range from about 350 to550 square meters/gram.

Example II PREPARATION OF NOBLE METAL-NHgBF4ALUMINA. CATALYST Aplatinum-alumina composition prepared essentially as described above inExample I, except that air was used for the complete calcinationprocedure, and containing about 0.6% platinum was employed in preparingthe noble metalNH BF alumina catalyst by the following procedure. 209grams of the calcined platinumalumina composition were placed in a1-liter 3-neck flask. The flask was connected through one neck to thehouse vacuum line and through another with a short length of Tygontubing to a buret. The third neck was stoppered. The flask was evacuatedand pumped with house vacuum for minutes. 12.05 grams (General Chemicaltechnical grade ammonium fiuoborate) were dissolved in DI water to make170 ml. of solution which were poured into the buret. The solution wasallowed to flow slowly into the flask while vacuum was still applied andthe catalyst was shaken vigorously. When all the solution had beenadmitted, the vacuum was broken. The catalyst was transferred to a 6crystallizing dish and dried in the forced air drying oven at 250 F. Thecatalyst was stirred occasionally while it was drying. The oven drycatalyst was placed in a cool muifle furnace, brought to 1000 F. andheld at that temperature for 2 hours. The catalyst was then removed fromthe furnace and cooled in a desiccator. The catalyst analyzed 5.31%volatile matter (1000 C.), 0.57% B, and 3.71% F.

Example III PREPARATION OF NOBLE METAIFH SIFG ALUMINA CATALYST Aplatinum-alumina composition prepared essentially as described above inExample I, except that air was used for the complete calcinationprocedure, and containing about 0.6% platinum was employed in preparingthe noble metalH SiF alumina catalyst by the following procedure. 209grams of calcined platinum-alumina composition were placed in a 1 liter3-neck flask. The flask was connected through one neck to house vacuumline and through another with a short length of Tygon tubingto a buret.The third neck was stoppered. The flask was pumped with house vacuum for10 minutes. The H SiF was diluted with DI water to make 170 ml. whichwere poured into the buret. The solution was allowed to flow slowly intothe flask while vacuum was still applied and the catalyst was shakenvigorously. When all the solution had been admitted, vacuum was broken.The catalyst was transferred to a 6" crystallizing dish and dried in theforced air drying oven at 250 F. The catalyst was stirred occasionallywhile it was drying. The oven dry catalyst was placed in a cool rnufllefurnace, brought to 1000 F., and held at that temperature for 2 hours.The catalyst was then removed from the furnace and cooled in adesiccator. The catalyst analyzed 4.85 percent volatile matter (1100 C.)and 2.7 percent F.

Example IV BREPAIGAT'IO-N OF vN O BlLE MET AL-Ni(B F4)2 ALUMINA CATALYSTA platinum-alumina composition prepared essentially as described abovein Example I except that air was used 6 for the complete calcinationprocedure, and containing about 0.6% platinum was employed in. preparingthe noble metal-Ni(BF -alumina catalyst by the following procedure(Prep. 805-3211).

209 grams of the platinum-alumina composition were weighed into aS-neck, 1 liter round bottom flask. One neck of the flask was stoppered,one neck attached to the closed stop-cock of a buret, and the third neckattached to a vacuum line. Ten minutes were allowed for removal of airfrom the flask and the catalyst. A solution of 16.7 g. of Ni(NO -6H Oand 12.05 g. of NH4BF dissolved in deionized water to make 170 ml. wasthen admitted through the buret. The flask and contents were shakenvigorously while the solution was being added. The catalyst wastransferred to a 6" crystallizing dish and placed in a forced-air dryingoven, set at 250 F., for about 16 hours. The oven-dried catalyst wasplaced in a sagger and heated in a muflie furnace 2 hours at 1000 F. Thecatalyst was cooled in a desiccator. Sample No. 500- K7030 Analysis:1.49% Ni, 0.57% B, 3.02% F.

Example V The isomerization process of the present invention isillustrated by Runs A, B, and C (illustrated below in Table I employingplatinum as the Group VIH metal). A catalyst prepared essentially asdescribed above in Example II was employed in Run A, a catalyst preparedessentially as described above in Example III was employed in Run B anda catalyst prepared essentially as described above in Example IV wasemployed in Run C. All runs were conducted under the conditionsspecified in the table which also shows the results of these runs.

TABLE I Run A B 0 Sample N o 5004,02 1 500-7, 038 500-7, 030 alystpercent 5. 31 4. F, percent 3.71 2. 70 B, percent... 0. 57 Isomerizationactivity:

Conditions Feedstock 650 680 650 300 300 300 3 2. 9 3 112/116 mol ratio3/1 3/1 3/1 Product 1 Pt-NH BF -alumina.

2 Pt-H SiF -alumina.

3 Pt-NKBFDaalumina.

The following data indicates that a platinum-alumina composition,prepared essentially as described above in Example I except that air wasused for the complete calcination procedure, containing promotercomponents in a combination of F and Sior BF provides better results inthe isomerization of n-pentane than the results provided by using any ofthese components alone. The results are based upon the isomerization ofn-pentane to isopentane under conditions, unless otherwise specified,including a temperature of 600 F., a pressure of 300 p.s.i.g., ahydrogen to hydrocarbon mole ratio of 3/1 and 1.5 WHSV. The data setsforth the particular promoter component employed with theplatinum-alumina composition and the results when a particular componentis employed. The relative activity is based upon a 0.6%platinum-alumina3.23% boria catalyst (Cat. No. 480279) as a referencestandard and was calculated using the following formula in which Krepresents the reaction rate constants:

7 Selectivity and conversion were calculated according to the formulae:Selectivity to LCFWX 100 Total conversion Total conversionzl-molepercent n-C remaining in the product 7. The method of claim 5 in whichthe noble metal is platinum and is about 0.1 to 2% of the catalyst.

8. The method of claim 5 in which the activated alumina is derived bycalcination of an alumina hydrate precursor consisting essentially ofabout 65 to 95% of alumina trihydrate and about 5 to 35% of a memberselected from the group consisting of amorphous hydrous Data PromoterTotal Selectivity, Relative Catalyst No. conversion, mole activity molepercent percent 4 Analysis Component percent 2.70% F, 0.6% SiO (est.)HQSIFB 1 61. 6 1 93. 465 0.20% '0 Si 02 7,030 1.5% Ni, 0.57% B, 3.02% FN1(BF4) 4 58.1 4 98.2 520 480-279. 3.23 0 B B1 3 27.9 100 100 1Evaluated at 680 F., 3 WHSV.

2 Excessive demethanation at 650 F. 3 Reference Catalyst: No. 480279.

4 Evaluated at 650 F., 3 WHSV.

What is claimed:

1. In a method of isomerizing a C -C n-paraflinic containing hydrocarbonfeed, the step comprising contacting said feed in the vapor phase with acatalyst at a temperature of about 500 to 750 F., superatmosphericpressure, and in the presence of free hydrogen, said catalyst consistingessentially of about 0.1 to 2% of a platinum group noble metal and NH BFon an activated alumina, said component being present in an amounteffective to enhance the activity of the catalyst.

2. The method of claim 1 in which the temperature is from about 600700F. and the n-paraffin is n-pentane.

3. The method of claim 1 in which the noble metal is platinum and isabout 0.1 to 2% of the catalyst.

4. The method of claim 1 in which the activated alumina is derived bycalcination of an alumina hydrate precursor consisting essentially ofabout 65 to 95% of alumina trihydrate and about 5 to 35% of a memberselected from the group consisting of amorphous hydrous alumina, aluminamonohydrate and their mixture and the activated alumina has an area ofabout 350 to 550 square meters per gram.

5. In a method of isomerizing a C to C n-paraffinic containinghydrocarbon feed, the step comprising contacting said feed in the vaporphase with a catalyst at a temperature of about 500 to 750 F.,superatmospheric pressure, and in the presence of free hydrogen, saidcatalyst consisting essentially of about 0.01 to 2% of a platinum groupnoble metal and Ni(BF on an activated alumina, said component beingpresent in an amount effective to enhance the activity of the catalyst.

6. The method of claim 5 in which the temperature is from about 600 to700 F. and the n-paraifin is n-pentane.

alumina, alumina monohydrate and their mixture and the activated aluminahas an area of about 350 to 550 square meters per gram.

9. In a method of isomerizing a C to C n-paraffinic containinghydrocarbon feed, the step comprising contacting said feed in the vaporphase with a catalyst at a temperature of about 500 to 750 F.,superatmospheric pressure, and in the presence of free hydrogen, saidcatalyst consisting essentially of about 0.01 to 2% of a platinum groupnoble metal and NH BF on an activated alumina, said NH BF being presentin a molar ratio with respect to said alumina of from about 0.001 to0.311.

10. In a method of isomerizing a C to C n-parafiinic containinghydrocarbon feed, the step comprising contacting said feed in the vaporphase with a catalyst at a temperature of about 500 to 750 F.,superatmospheric pressure, and in the presence of free hydrogen, saidcatalyst consisting essentially of about 0.01 to 2% of a platinum groupnoble metal and Ni(BF on an activated alumina, said Ni(BF being presentin a molar ratio with respect to said alumina of from about 0.001 to 0.31.

References Cited by the Examiner UNITED STATES PATENTS 2,483,130 9/49Garrison 25244l 2,838,444 6/58 Teter et al. 252-441 2,852,472 9/58Barrett 208-139 X 2,935,545 5/60 Block et al 260683.66 2,951,889 9/60Geerts et al 260-683.66 2,999,074 9/61 Bloch et al. 252441 X ALPHONSO D.SULLIVAN, Primary Examiner.

1. IN A METHOD OF ISOMERIZING A C4-C9 N-PARAFFINIC CONTAININGHYDROCARBON FEED, THE STEP COMPRISING CONTACTING SAID FEED IN THE VAPORPHASE WITH A CATALYST AT A TEMPERATURE OF ABOUT 500 TO 750*F.,SUPERATMOSPHERIC PRESSURE, AND IN THE PRESENCE OF FREE HYDROGEN, SAIDCATALYST CONSISTING ESSENTIALLY OF ABOUT 0.1 TO 2% OF A PLATINUM GROUPNOBLE METAL AND NH4BF4 ON AN ACTIVATED ALUMINA, SAID COMPONENT BEINGPRESENT IN AN AMOUNT EFFECTIVE TO ENHANCE THE ACTIVITY OF THE CATALYST.5. IN A METHOD OF ISOMERIZING A C4 TO C9 N-PARAFFNIC CONTAININGHYDROCARBON FEED, THE STEP COMPRISING CONTACTING SAID FEED IN THE VAPORPHASE WITH A CATALYST AT A TEMPERATURE OF ABOUT 500 TO 750*F.,SUPERATMOSPHERIC PRESSURE, AND IN THE PRESENCE OF FREE HYDROGEN, SAIDCATALYST CONSISTING ESSENTIALLY OF ABOUT 0.01 TO 2% OF A PLATINUM GROUPNOBLE METAL AND NI(BF4)2 ON AN ACTIVATED ALUMINA, SAID COMPONENT BEINGPRESENT IN AN AMOUNT EFFECTIVE TO ENHANCE THE ACTIVITY OF THE CATALYST